(1) Field of the Invention
The present invention relates to an apparatus, and method for so using, ultrasonic and RF signals to establish the position of a moveable platform. More specifically, the present invention relates to a method of situating transceiver and transponder modules so as to measure the position of an elevator car in operation.
(2) Description of Related Art
A Positioning Reference System (PRS) is a component of an elevator control system that provides fast and accurate position measurement of elevator car in a hoistway. The speed and accuracy of the measurement is determined by the given elevator control system in accordance with a prescribed level of ride quality. For example, it is typically a requirement that the position measurement should be performed within a 10 ms lag and to a 1 mm accuracy. Considering the wide operating range (up to 500 m) of elevators, these performance requirements can be difficult to achieve. In addition to the performance requirements on accuracy and measurement lag, a minimized correction run is the other important performance requirement. Here, ‘minimized’ means less than one-floor distance.
Many existing PRSs are based on encoders that are attached to the elevator motor, governor, or independent sheaves. These PRSs suffer from differences between the encoder reading and the real position that is caused by slippage, rope stretch, mechanical wear in subsystems, and/or building sway. To minimize the difference, correction should be performed frequently based on some fixed and known referencing points showing the real position of landing floor and leveling-zone. A vane system, consisting of vane reader and vanes, provides these referencing points and their detection means. Considering the simple functionality of the vane system, the vane system is quite cost-inefficient since a vane, which is installed at every floor by a mechanic in the hoistway, costs $10 for material, 0.5 hour for installation, and about 0.1 hour for adjustment. Overall, one of the most significant problems in the existing PRSs is the poor performance to cost ratio.
What is therefore needed, is a high-accuracy positioning means with low cost for material, installation, and maintenance.